The Air Force’s new T-7 Red Hawk training jet flew for the first time Wednesday in St. Louis, Missouri, the company said in a release.

Its flight marks the beginning of the T-7′s final development phase before Boeing starts producing military-ready jets. Red Hawks will replace the Air Force’s six-decade-old T-38 Talon trainers as the main platform that prepares American and foreign pilots to fly fighter and bomber aircraft.

Over the course of the hour-long trip from St. Louis Lambert International Airport, Maj. Bryce Turner, a test pilot with the 416th Test Squadron at Edwards Air Force Base in California, and Steve Schmidt, Boeing’s chief T-7 test pilot, gauged how smoothly the plane maneuvered and tested secondary systems like the auxiliary power supply, Boeing spokesperson Randy Jackson said.

The pair vetted how well the plane handled positive and negative g forces, as a pilot experiences when accelerating or flying upside down, and practiced in high-altitude airspace, Jackson said.

“The stable performance of the aircraft and its advanced cockpit and systems are game-changers for U.S. Air Force student pilots and instructors alike,” Turner said in the release.

As the first Air Force training jet designed in the 21st century, the T-7 offers students a digital cockpit, more realistic simulators and software that can be updated as real-world threats evolve.

The airframe that flew Wednesday is one of five test aircraft that will be delivered to the Air Force before it starts receiving fully finished jets at its schoolhouses. The Air Force plans to buy 351 Red Hawks starting in December 2025 under a $9.2 billion contract awarded in 2018.

But design problems with the escape system and ejection seat have set the production timeline back by multiple years.

Air Force officials now plan to decide in early 2025 whether to begin building operational jets, meaning the service would start receiving aircraft two years later than originally intended.

Some problems stem from an effort to make the jet more accessible to pilots of any race or sex. Earlier airframes were primarily designed to accommodate men based on body measurements from decades-old military studies. That means many women’s torsos or arms are too short to safely operate the jets or to eject.

The Air Force has said that testing showed T-7 pilots could be at high risk for concussions, unsafely speeding up when their parachutes open, or losing their visor. Further tests earlier this year aimed to resolve those concerns.

Jackson said a successful high-speed test in February laid the groundwork for future rounds to ensure the escape system is safe, but did not say whether specific issues remain.

Boeing claimed in the release that the T-7′s cockpit egress system is the “safest of any trainer.”

“This first flight with the Air Force represents our team’s commitment to delivering a new level of safety and training for fighter and bomber pilots,” said Evelyn Moore, Boeing’s T-7 program manager, in the release. “We remain focused on engineering ways to better prepare warfighters for changing mission demands and emerging threats.”

Meanwhile, T-38 maintenance issues have slowed the training pipeline amid a longstanding fighter pilot shortage.

Air Force Times reported in March that a private contractor’s delays in restoring the T-38′s J85 engines threatened to slow pilot production for at least another six months. The engine enterprise may not fully recover until April 2024, despite improvements in the supply of spare parts and repair rates, the service said.

“It’s an old engine. … There’s a lot of moving parts,” Air Education and Training Command boss Lt. Gen. Brian Robinson said Feb. 16. “But as a customer, I just want to produce pilots.”